1. Field of the Invention
The present invention relates generally to water based polishing slurries, comprising oxide polishing particles. More specifically, the polishing slurries of the present invention comprise an innovative (multi-modal) particle distribution for improved polishing performance.
2. Discussion of the Prior Art
U.S. Pat. No. 5,626,715 to Rostoker describes an aluminum oxide particle distribution for use in polishing semiconductor substrates. Although the methods described in Rostoker are useful, they are increasingly inadequate in meeting the ever increasing demands of the semiconductor industry. The slurries of Rostoker do not provide the efficiency and selectivity which are now possible in accordance with the present invention.
The slurries of the present invention comprise slurry particles in which at least 90 weight percent, more preferably at least 95 weight percent, yet more preferably at least 98 weight percent, yet more preferably at least 99.5 weight percent and yet more preferably 100 weight percent of the particles are within the range of 10 nanometers to 500 nanometers, more preferably 10 nanometers to 400 nanometers, yet more preferably 10 nanometers to 300 nanometers and yet more preferably 10 nanometers to 100 nanometers.
The slurry particles of the present invention are preferably oxides, particularly ceria, alumina and/or silica. The slurry particles of the present invention are further defined as having a multi-modal size distribution, comprising a first size distribution curve having a first asymptote indicating a first particle size and a second distribution curve adjacent or overlapping (preferably adjacent) the first distribution curve, the second distribution curve having a second asymptote indicating a larger particle size. The large particle size (second asymptote) divided by the small particle size (first asymptote) is preferably in the range of 1.05-5000 more preferably 1.1-1000, yet more preferably 1.5-500 and yet more preferably 2-100.
It has been surprisingly discovered that such a multi-modal particle distribution provides improved polishing performance, because improved particle packing at the polishing interface is possible. Furthermore, the polishing slurries of the present invention tend to have less (lot-to-lot) performance variability, relative to many conventional mono-modal slurries, because variability in each distribution curve tend to cancel each other out as particles representing multiple distribution curves are combined, provided particles near the extremes (10 nanometers and 600 nanometers) are kept to a minimum.